The terminate() function (C++ only)

In some cases, the exception handling mechanism fails and a call to void terminate() is made. This terminate() call occurs in any of the following situations:

• The exception handling mechanism cannot find a handler for a thrown exception. The following cases are more specific:
  • During stack unwinding, a destructor throws an exception and that exception is not handled.
  • The expression that is thrown also throws an exception, and that exception is not handled.
  • The constructor or destructor of a nonlocal static object throws an exception, and the exception is not handled.
  • A function registered with atexit() throws an exception, and the exception is not handled. The following demonstrates this:
• A throw expression without an operand tries to rethrow an exception, and no exception is presently being handled.
• A function f() throws an exception that violates its exception specification. The unexpected() function then throws an exception which violates the exception specification of f(), and the exception specification of f() did not include the class std::bad_exception.
• The default value of unexpected_handler is called.

The following example demonstrates that if a function registered with atexit() throws an exception and the exception is not handled, an invocation to void terminate() is made.

extern "C" printf(char* ...);
#include <exception>
#include <cstdlib>
using namespace std;

extern "C" void f() {
  printf("Function f()\n");
  throw "Exception thrown from f()";
}

extern "C" void g() { printf("Function g()\n"); }
extern "C" void h() { printf("Function h()\n"); }

void my_terminate() {
  printf("Call to my_terminate\n");
  abort();
}

int main() {
  set_terminate(my_terminate);
  atexit(f);
  atexit(g);
  atexit(h);
  printf("In main\n");
}

See the output of the above example:

In main
Function h()
Function g()
Function f()
Call to my_terminate

To register a function with atexit(), you pass a parameter to atexit() a pointer to the function you want to register. At normal program termination, atexit() calls the functions you have registered with no arguments in reverse order. The atexit() function is in the <cstdlib> library.